It is considered desirable for cigarettes to provide relatively low levels of tar in the cigarette smoke entering the smoker's mouth. This result is achieved by the utilization of filtration, air dilution or, most commonly, a combination of the two.
Generally, as the tar level falls, so does the flavour level in the cigarette smoke. It is considered desirable to increase the flavour level of smoke entering the mouth of the smoker for the same tar level and this can be achieved to some extent by using more highly-flavored tobaccos.
However, serious limitations exist with the current technology. There is an upper level of venting of the cigarette which is possible before the cigarette smoke becomes "airy" and, in addition, there is an upper pressure drop limitation associated with conventional filter material.
It is known from U.S. Pat. No. 3,882,877, assigned to the assignee hereof and the disclosure of which is incorporated herein by reference, to place a disc of microfine fibers between two filter rod segments of conventional tow material in a cigarette smoke filter. However, in use, this type of filter exhibits a tendency to plug and inhibit the flow of cigarette smoke through the filter.